The invention relates to a temperature control device for soldering equipment.
From EP 0,048,772 a temperature control device for a hot gas soldering and unsoldering device is known in which the gas, such as air, is directed from a gas source through an elongated heat coil which heats the gas and guides it via a nozzle to the object to be heated, such as a soldering spot, at a temperature corresponding to the desired application. At that time, the gas flowing through the heat coils forms a heat output transmission device from the heat coil to the soldering spot. With this hot gas device, the heat coil has a positive temperature coefficient and it is fed by a controllable heating current source, the current of which is periodically interrupted. During the interruption of the heating current, a measuring current is directed from a measuring current source through the heat coils, wherein the voltage drop along the heat coil is a function of the resistance and thus of the temperature of this heat coil. This voltage drop is compared with a control value and is used via a control circuit for the control of the controllable heating current source. This type of temperature control is relatively inertia-free and precise due to the low heating capacity of the heat coil and it is possible, during operational pauses, to interrupt the gas flow through the heat coils without interrupting the heating current as well, since the heating coil, due to the temperature control device, is always maintained at the temperature predetermined by the control value without the danger of a burnout of the heat coil. Furthermore, the heat coil, during renewed feeding of the gas flow, is at its operating temperature so that the gas flow is immediately heated to the desired temperature. Since the gas forming the heat output transmission device is directed to the soldering spot, however, changes in the temperature of the hot gas may occur during passage through the nozzle, particularly in the case of certain cross sections and forms of the nozzle. These temperature changes cannot be determined by taking temperature measurements along the heat coil and may lead to changes in the exit temperature of the hot gas from the nozzle.
Furthermore, from EP-0,202,401, a soldering or unsoldering device is known in which the heat output transmission device is formed by a soldering point and the heating arrangement includes a heat coil with a negligible temperature coefficient and a temperature sensor which is serially connected with this heat coil and is in the form of an additional heat coil section with a measurable temperature coefficient. Also here, during a periodic interruption of the heating current, the voltage drop occurring along the combination of the heat coil and the temperature sensor, is measured, compared with a control value and is used via a control circuit for controlling a controllable heating source which feeds the named combination. When the soldering tip, forming the heat output transmission device, is relatively long or has a relatively high heat resistance, then the temperature measurement taking place in the area of the heating device permits no clear information regarding the temperature present at the active end of the soldering tip that comes into contact with the soldering spot, i.e., particularly not when, at this end, a very large heat loss occurs.
In order to improve the precision of the temperature control, it is furthermore known that with soldering devices, arranging a temperature sensor which is separate from the heat coil and has the smallest possible dimensions inside the soldering tip is beneficial, as far as possible towards the active end of this soldering tip. Since in this case, the temperature sensor is connected with the heat coil in a heat-conducting manner only via the soldering tip, there exists, during a change of the soldering tip without prior turning off of the soldering device, the danger of overheating and a burnout of the heat coil since the temperature sensor then indicates a temperature which lies considerably below the actual temperature of the heat coil and leads to an increase of the heating current.
Furthermore, in the case of a very strong heat output at the soldering tip, during soldering of large-surface components with a high heat capacity, there arises the problem that, during the soldering process, the heat coil is brought to a relatively high temperature in order to deliver the required heat output to the soldering spot. When the soldering tip is then moved away from the soldering spot, the high heat energy still stored in the heat coil leads to an overheating of the soldering tip with all sorts of disadvantageous consequences, such as overheating of the solder located thereon or the oxidation of the soldering tip itself.